Rotary encoders have been recently used for input sections, such as menu selectors and volume controllers of various electronic devices, such as car audio systems. The rotary encoders have been required to have small sizes and to control the devices precisely.
FIGS. 10 and 11 are a cross-sectional view and an exploded perspective view of conventional rotary encoder 501 disclosed in JP11-135310, respectively. Operation shaft 6 is made of molding resin and has center columnar section 6A having a circular column shape and annular flange 6B protruding from the outer circumference of center columnar section 6A. The upper part of center columnar section 6A has cutout 6C therein adapted for engagement in an operation dial. An upper surface of annular flange 6B has click grooves 6D extending radially. A caulking protrusion being crushed, slidable brush 8 is fixed to a lower surface of annular flange 6B.
Shaft supporter 9 is made of resin and has protruding section 9A having an octagonal columnar shape, and flat plate section 9B having an octagonal shape and protruding from an outer circumference of protruding section 9A. Cylindrical hole 9C having a cylindrical shape is provided in a center of shaft supporter 9 to penetrate shaft supporter 9. Center columnar section 6A of operation shaft 6 is inserted into cylindrical hole 9C. A caulking protrusion is crushed to fix click spring 10 to a lower surface of flat plate section 9B.
Center columnar section 6A of operation shaft 6 is inserted into circular hole 10A provided in a center of click spring 10. A spring 10B is provide along an outer circumference of circular hole 10A. Spring 10B elastically contacts click grooves 6D provided in the upper surface of annular flange 6B.
Case 1 is made of resin and has recess 1B therein opening upward. Center hole 1A is provided in a center of a bottom surface of recess 1B. A circular columnar protrusion provided at a center of a lower surface of operation shaft 6 is inserted into center hole 1A. Case 1 supports operation shaft 6 rotatably.
Attachment bracket 7 has a squared U-shape and has a center hole. While protruding section 9A of shaft supporter 9 protrudes upward from the center hole, attachment bracket 7 has legs 7A to sandwich shaft supporter 9 and case 1 stacked on each other from above shaft supporter 9. Tips of legs 7A are bent at a lower surface of case 1 to accommodate operation shaft 6 and slidable brush 8 between shaft supporter 9 and case 1.
FIG. 12 is a top view of case 1 of rotary encoder 501. Center hole 1A has a circular shape having center 1D. Common contact 2 and signal contact patterns 3 and 4 are fixed to a bottom surface of recess 1B by insert molding along circular circumference 1E about center 1D of center hole 1A. Common contact 2 and signal contact patterns 3 and 4 are arranged in arcuate shapes on circumference 1E.
As shown in FIG. 12, signal contact pattern 3 includes signal contacts 3A to 3F connected electrically with each other. Signal contact pattern 4 includes signal contacts 4A to 4F connected electrically with each other. Signal contact patterns 3 and 4 and common contact 2 are embedded in the bottom surface of recess 1B of case 1 so that upper surfaces of signal contacts 3A to 3F and 4A to 4F and upper surface of common contact 2 are flush with the bottom surface of recess 1B of case 1. Signal contacts 3A to 3F and 4A to 4F are provided on circumference 1E. Signal contacts 3A to 3F are arranged on circumference 1E within an angular range smaller than 180 degrees about center 1D. Signal contacts 4A to 4F are arranged on circumference 1E within an angular range smaller than 180 degrees about center 1D. The angular range having the signal contacts 3A to 3F arranged therein is away from the angular range having signal contacts 4A to 4F arranged therein, that is, does not overlap the angular range having signal contacts 4A to 4F arranged therein. Common contact 2 has an arcuate shape on circumference 1E. A center angle of the arcuate shape of common contact 2 is larger than the angular range having signal contacts 3A to 3F arranged therein and the angular range having signal contacts 4A to 4F arranged therein. Signal contact pattern 3, signal contact pattern 4, and common contact 2 are electrically insulated from each other, and are connected to terminals 11A, 11B, and 11C extending to an outside of case 1, respectively.
FIG. 13 is a top view of case 1 having rotary encoder 501 having slidable brush 8 arranged thereon. Slidable brush 8 is made of conductive elastic metal plate and is rotatable about center 1D. Slidable brush 8 has contacting sections 81A, 81C, 81E, and 81G arranged with angular intervals of 90 degrees about center 1D, and contacting sections 81B, 81D, 81F, and 81H located further inward than contacting sections 81A, 81C, 81E, and 81G, respectively.
An operation of conventional rotary encoder 501 will be described below.
Upon operation shaft 6 rotating, slidable brush 8 fixed to the lower surface of annular flange 6B of operation shaft 6 rotates. The rotation of slidable brush 8 causes contacting sections 81A to 81H to slide on the bottom surface of recess 1B of case 1 along circumference 1E. Then, contacting sections 81A to 81H contact and are removed from signal contacts 3A to 3F and 4A to 4F and common contact 2. The center angle of the arcuate shape of common contact 2 along circumference 1E is larger than 90 degrees. Thus, regardless of the angular position of slidable brush 8, at least two of contacting sections 81A to 81H contact common contact 2, that is, slidable brush 8 contacts common contact 2.
The angular range having signal contacts 3A to 3F arranged therein is smaller than 90 degrees, and the angular range having signal contacts 4A to 4F arranged therein is smaller than 90 degrees. Each of contacting sections 81A and 81B simultaneously contacts one of signal contacts 3A to 3F and 4A to 4F and common contact 2. Similarly, each of contacting sections 81C and 81D simultaneously contacts one of signal contacts 3A to 3F and 4A to 4F and common contact 2. Similarly, each of contacting sections 81E and 81F simultaneously contacts one of signal contacts 3A to 3F and 4A to 4F and common contact 2. Similarly, each of contacting sections 81G and 81H simultaneously contacts one of signal contacts 3A to 3F and 4A to 4F and common contact 2. Four contacting sections 81A, 81C, 81E, and 81G are arranged at the angular intervals of 90 degrees, and four contacting sections 81B, 81D, 81F, and 81H are arranged at the angular interval of 90 degrees. This arrangement causes each of six signal contacts 3A to 3F to contact and be removed from common contact 2 via slidable brush 8 repetitively four times while operation shaft 6 rotates by 360 degrees. Since signal contacts 3A to 3F are connected electrically with each other as signal contact pattern 3, signal contact pattern 3 is connected to and disconnected from common contact 2 repetitively 24 times while operation shaft 6 rotates by 360 degrees. Similarly, each of six signal contacts 4A to 4F contact and are removed from common contact 2 via slidable brush 8 repetitively 4 times while operation shaft 6 rotates by 360 degrees to rotate slidable brush 8 by 360 degrees. Since signal contacts 4A to 4F are connected electrically with each other as signal contact pattern 4, signal contact pattern 4 is connected to and disconnected from common contact 2 repetitively 24 times while operation shaft rotates by 360 degrees. Thus, rotary encoder 501 outputs rectangular wave A501 having 24 peaks between terminals 11A and 11B due to the connection and disconnection between common contact 2 and signal contact pattern 3 while operation shaft 6 rotates by 360 degrees. Similarly, rotary encoder 501 outputs rectangular wave A502 having 24 peaks between terminals 11A and 11C due to the connection and disconnection between common contact 2 and signal contact pattern 4 while operation shaft 6 rotates by 360 degrees.
The operation dial attached to operation shaft 6 is rotated to input rectangular waves A501 and A502 to a controller implemented by e.g. a microcomputer. Rotary encoder 501 is connected to the controller and is used e.g. to adjust the volume of a car audio system. In this case, the controller detects, based on rectangular waves A501 and A502, a rotation direction and a rotation angle of the operation dial (i.e., operation shaft 6) to control the volume of the car audio system.
FIG. 14A illustrates rectangular waves A501 and A502 output from rotary encoder 501. In FIG. 14A, rectangular waves A501 and A502 are shown by the turning on and off of a switch provided between common contact 2 and signal contact pattern 3 and by the turning on and off of a switch formed between common contact 2 and signal contact pattern 4, respectively. The angular positions and angular widths of signal contacts 3A to 3F and 4A to 4F are determined such that rectangular waves A501 and A502 are output with a phase difference of 90 degrees. The combination of respective statuses of rectangular waves A501 and A502 provides four angular ranges θ501 to θ504: (1) angular range θ501 in which rectangular wave A501 represents the turning on and rectangular wave A502 represents the turning off; (2) angular range θ502 in which rectangular waves A501 and A502 represent the turning on; (3) angular range θ503 in which rectangular wave A501 represents the turning off, and rectangular wave A502 represents the turning on; and (4) angular range θ504 in which rectangular waves A501 and A502 represent the turning off. Based on the order of angular ranges θ501 to θ504, the controller determines a rotation direction of operation shaft 6 and counts the number of the peaks of rectangular waves A501 and A502. The controller controls a controllable object based on the rotation direction and the number of the peaks. In the case that the object is the volume of the car audio system, the controller determines, based on the rotation direction, a changing direction along which the volume is increased or decreased. The controller further determines a change amount based on the number of the peaks. Then, the controller changes the volume by the determined change amount in the determined changing direction.
The widths of angular ranges θ501 to θ504 depend on the widths of signal contacts 3A to 3D and 4A to 4D along circumference 1E. Signal contact patterns 3 and 4 are formed by punching a metal plate using dies designed to provide predetermined widths of angular ranges θ501 to θ504. Rotary encoder 501 includes signal contact patterns 3 and 4 formed by the punching and embedded in the bottom surface of case 1. Rotary encoder 501 may output waveforms different from the waveforms shown in FIG. 14A. FIG. 14B shows rectangular waves A511 and A512 output from rotary encoder 501 including signal contact patterns 3 and 4 formed by the punching, instead of rectangular waves A501 and A502 shown in FIG. 14A. Angular ranges θ511, θ512, θ513, and θ514 shown in FIG. 14B represent statuses of the turning on and off as angular ranges θ501, θ502, θ503, and θ504 shown in FIG. 14A, respectively. As shown in FIG. 14A, angular ranges θ501 to θ504 are equal to each other ideally. However, angular range θ512 is particularly narrow out of angular ranges θ511, θ512, θ513, and θ514 actually, as shown in FIG. 14B. Therefore, upon operation shaft 6 rotating, the microcomputer may not read angular range θ512 if a duration in which contacting sections 81A to 81H of slidable brush 8 slide on in angular range θ512 is excessively short.
FIG. 15 is a cross-sectional view of signal contact 3A (3B to 3F and 4A to 4F) of rotary encoder 501 along circumference 1E. Signal contacts 3A to 3F and 4A to 4F of signal contact patterns 3 and 4 are formed by punching out the metal plate. When the metal plate for forming signal contact 3A is punched out with a die, the die pulls an edge of an upper surface of signal contact 3 in a punching direction, and thus, deforms signal contact 3, thereby producing shear drop portion 14B at the edge of the upper surface. Shear drop portion 14B has a round shape like chamfering the edge of the upper surface. The lower surface of signal contact 3A has burr 14C produced by pulling a part of the metal downward with the die. Width L1 of surface 14A of signal contact 3A exposed on the bottom surface of recess 1B is smaller than width L2 of signal contact 3A. This structure causes the resin of case 1 to cover shear drop portion 14B of signal contact 3A. Width L2 of signal contact 3A is determined to provide the predetermined lengths of angular ranges θ501 to θ504. However, width L1 of surface 14A of signal contact 3A exposed on the bottom surface of recess 1B of case 1 is smaller than determined width L2 of signal contact 3A. Thus, the angular range in which slidable brush 8 contacts signal contact 3A during the rotation of operation shaft 6 is smaller than the predetermined angular range. This reduces the angular ranges in which the switches formed between common contact 2 and signal contact pattern 3 and between common contact 2 and signal contact pattern 4 are turned on. Angular range θ512 in which rectangular waves A511 and A512 represent the turning on is accordingly shorter than other angular ranges θ511, θ513, and θ514, as shown in FIG. 14B.
Under a demand to have a smaller size and operate precisely, rotary encoder 501 is demanded to have smaller widths of signal contacts 3A to 3F and 4A to 4F and smaller intervals between signal contacts 3A to 3F and 4A to 4F. The shape of shear drop portion 14B of signal contacts 3A to 3D and 4A to 4D changes depending on material of the metal plate or conditions of the punching, thus being unpredictable. Thus, shear drop portion 14B may be a factor preventing rotary encoder 501 from having a small size and operating precisely.